1. Field of the Invention
The present invention relates to a method for manufacturing a printed circuit board and, more particularly, to a manufacturing method using a metal protection layer to protect the circuit inside a cavity and other regions containing no circuit in the printed circuit board when using a laser manufacturing process to manufacture the cavity.
2. Description of the Related Art
In a current printed circuit board manufacturing process, lasers (such as carbon dioxide lasers, CO2 lasers) are often used for processing like cutting or drilling. Compared with traditional machining, lasers can provide advantages such as high processing speed and high precision. Generally, in a printed circuit board, no circuit layout is implemented in a cavity thereof. Therefore, lasers can be used for forming a cavity in the printed circuit board. However, if it is necessary to implement a circuit layout in the cavity, regions containing no circuit in the cavity could be damaged due to the laser processing.
In a prior art technique, a protection mask film (PMF) is attached to the bottom layer of the region wherein the cavity is formed to protect the patterned circuit of the cavity. However, since the PMF is made of a polymer material and is not resistant to heat generated in the laser process, the PMF is likely to be damaged by the laser and so is the circuit around the cavity when the cavity is formed. Furthermore, it takes a lot of labor, time, and costs for workers to manually attach the PMF and to rip off the residual PMF after the cavity is formed.
Japanese Patent Application No. 10-22645 discloses a process for manufacturing a printed circuit board with a cavity. The process comprises forming a curable organic material or Teflon layer on the base board and then forming a patterned protection layer. However, the circuit pattern is formed by a traditional cutting process, with which it is difficult to achieve high precision. In addition, if a laser manufacturing process is used, problems arise in the organic layer which is still vulnerable to the high heat generated by the laser, and the circuit around the cavity could be damaged as well.
Therefore, it is necessary to provide a method for manufacturing a printed circuit board to solve the problems presented in the prior art techniques.